If the current is too great, the filament will melt, or blow out, causing the circuit to become open. But we want more than one light to shine on our Christmas tree or along the roofs of our homes. If you want to connect multiple light bulbs to the same power source, there are two ways to do that: either attach the lights in series or in parallel.
When lights are attached in series, the electricity passes from the power source to the first light, and then from light to light until it returns to the power source. In this setup, when a filament within any one bulb blows out, it creates an open circuit in the wiring. As we mentioned earlier, when a circuit is incomplete, or open, electricity fails to pass through any of the wire, causing all the lights to go out.
When lights are attached in parallel, each light is on its own circuit to the power source. If one filament burns out, it has no effect on the remaining lights, as they each continue to be in a closed circuit with the power source. Check out the difference. With strings of holiday lights, engineers decided that the best option was to connect several series of lights together in parallel.
In other words, holiday lights are both in series and in parallel. This way, when one series of bulbs becomes defective -- say, from a loose bulb -- it should have no effect on any of the other series of bulbs, since they are in parallel to the defective series.
This is why sometimes only one portion of your lights will become defective, while others will remain functional. When additional strings of lights are attached to the end of a string, these lights are added in parallel to the original strand.
But what about when a bulb goes out in a series? It used to be that when one bulb went out, the entire series would go out. If this were the case, you would have to check each bulb individually to see which one was blown out.
If multiple bulbs were blown out, this would become exceedingly difficult. A shunt is any device that allows current to continue flowing through a circuit by creating a path of lower resistance than the original path.
In incandescent holiday lights, shunts are small wires wrapped beneath the filament. Initially, they are coated with a substance that makes them an insulator. In other words, electricity cannot pass across the shunt as long as the filament exists, because the coating gives the shunt a higher resistance initially than the filament, and the electrical current avoids the shunt in order to find the path of least resistance through the filament.
If the filament burns out, however, the high temperature from the burnout will cause the substance coating the shunt to melt off, revealing the lower resistance wire beneath. As the electrical current within a wire increases, the wire can heat up, at times causing melting or even fires.
When the current increases past a safe level, instead of the wire melting or your Christmas tree catching fire, the fuse safely breaks the circuit, averting many disastrous scenarios. Fuses are typically small sections of replaceable wire, rated to a maximum current level.
Because they are more delicate than the rest of the wiring, a fuse will burn out before overcurrent has an opportunity to overheat other portions of the light strand. When a fuse breaks, the circuit becomes incomplete and current cannot flow through the remainder of the circuit.
If only one section of your lights become extinguished, this means that the circuit is open on that particular series. If this happens, there are a few things that could be going on. First off, you could simply have a loose bulb. This is a common problem, and the most easy to identify and fix, by simply screwing back in the bulb. Second, it could mean that one or more lights have blown out but that the shunt is defective, possibly from the insulating substance remaining intact.
Finally, there could be something defective in the wiring, causing the series to become an open circuit. If only one light goes out, it almost certainly means that individual light is defective and needs to be replaced. This is the most common problem and the easiest to identify and fix. If this happens it is important to replace the bulbs quickly. When the filament of a bulb burns out and the shunt takes over, it has a lower resistance than the filament. As a result, each remaining bulb gets slightly brighter, burns a little hotter and burns out more quickly.
As each bulb burns out, and the volts from the power source is distributed to fewer and fewer bulbs, this process happens faster and faster. The last few bulbs will burn out very quickly. So it is best to replace burnt-out bulbs quickly when they go out. If all of your lights go out, it is probably because you have too great a current coming from the power source and have blown a fuse. If, after replacing the fuse, fuses continue to blow, it could be because you have too many bulbs burned out or too many strands of lights connected to the same socket.
This is called overloading a circuit. You could continue to replace fuses — but a blown fuse is typically a sign that some issue is causing too great of a current to pass through the fuse. Christmas lights are a big part of the holiday season. As November and December roll around, you might see strands of lights everywhere -- on Christmas trees , houses, shrubs, bushes and even the occasional car!
Have you ever wondered how these lights work? Why is it that if you pull out or break one of the bulbs, the whole strand of lights goes out? And how do they create the lights that sequence in different color patterns? Each bulb was a 5- or watt bulb like the bulb you find in a night light. You can still find strands of these bulbs today, but they aren't very common anymore for three reasons:.
The one advantage of this arrangement is that a bulb failure has absolutely no impact on the rest of the bulbs. That's because a volt bulb system places the bulbs in parallel , like this:. You can have two, 20 or bulbs in a strand that is wired in parallel.
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